FIGS. 17 to 19 are vertical sectional views of conventional magnet couplings respectively. FIG. 17 shows a synchronous type magnet coupling in which magnets 3 and 4, each consisting of permanent magnets alternately different in polarity, are disposed on the peripheries of the respective end faces of a drive-side yoke 1 and a load-side yoke 2 which are rotatably supported, so that torque is transferred only when the yokes 1 and 2 rotate synchronously. FIG. 18 shows a hysteresis magnet coupling in which a magnet 3 and an isotropic magnet 34 are used on the drive and load sides respectively to transfer a predetermined torque independently of the number of revolutions. FIG. 19 shows an eddy current magnet coupling in which a magnet 3 is employed on the drive side, while a magnetic material such as carbon steel or cast iron is employed on the load side. In these magnet couplings, the drive side and the load side are spaced apart from each other, and an isolating plate 5 is disposed in the illustrated gap G between the drive and load sides so that the drive side is not affected by the load-side environment.
As illustrated, keyways are cut in respective central bores 8 and 9 of the yokes 1 and 2, and drive and driven shafts are fitted into these keyways and thus rotatably supported by the axially outer portions, respectively, of the magnet coupling.
In all of these magnet couplings the smaller the illustrated gap G, the greater the value of transferred torque. However, in the conventional magnet couplings, the isolating plate 5, which isolates the drive and load sides from each other, involves deviations in terms of the machining accuracy and the axial center, and each of the members of the magnet coupling on the drive and driven sides is supported in a cantilever manner, which means that the support conditions are inferior and readily affected by wear of bearings or the like. Accordingly, the gap G is generally set at 5 to 10 mm, modally a value close to 10 mm. It is particularly difficult to produce the eddy current coupling shown in FIG. 19, because the control of the gap is effected through a non-magnetic disk plate 35, and the transferred torque is particularly weak in this case.
10 In the prior art it is necessary to provide gaps between the isolating plate 5 and the drive-side magnet 3 and the isolating plate 5 and the load-side driven magnet 4 or magnetic yoke 2, respectively, and the drive- and load-side rotary members cannot be rotatably supported at the sides thereof which are closer to the isolating plate 5. Accordingly, the size of the device is unavoidably increased in its axial direction, because of to the structures of bearings for thrust and radial directions which support the attraction forces on the drive and load sides of the magnet coupling, or the bearing portions complicate the arrangement of the device. In a device which handles a fluid, for example, a pump, the bearing portion interferes with the flow path resulting in problems such as an increase in the fluid resistance.